The present disclosure relates to a fixing device for fusing and fixing an unfixed toner on a recording medium onto a sheet and an image forming apparatus, such as a copying machine, a printer and a facsimile, including this fixing device.
An image forming apparatus of an electrographic manner, such as a copying machine or a printer, includes a fixing device for fixing a toner image onto a recording medium, such as a sheet. In the fixing device, considering worm-up time shortening and energy saving, as a heat source fusing a toner, a heat source in an induction heating (IH) manner is applied. The heat source in the IH manner makes magnetic flux generated by a coil act on a heating member, such as a fixing belt, to heat the heating member. The coil is configured to be wound along a rotation axial direction of the heating member outside the heating member and coil configuration of such a form is called as a “external capsuling type (axial direction wound) coil”. The external capsuling type coil is formed in a shape along a curved face of the heating member, thereby maintaining a distance between the coil and the heating member constant to secure heat generation performance of the heating member.
The heating member is configured so that the fixing belt is put between an internal member of the fixing belt and an external pressuring roller and parts the fixing belt and the internal member are slid to rotate the fixing belt. The IH manner using such a sliding belt is called as a sliding belt IH manner. In the sliding belt IH manner, by suitably designing function-separation of the internal member of the fixing belt, the fixing device having low heat capacity and shortening the worm-up time is achieved. In the fixing device in the sliding belt IH manner, electrical components, such as a thermostat or a thermistor, can be located inside the fixing belt.
For example, an image heading device in an electromagnetic induction heating manner using a heating belt is known. Then, a temperature sensor is located at a location having a highest heating value in a heating belt and, in an area at where a magnetic field of the heating belt is weakened by a coil, opening widths of an internal core and a pressuring stay are made narrower than an inside width of the coil, and a signal line is located inside the internal core.
Moreover, a fixing device bringing an unfixed toner image into contact with an endless fixing belt and heating and fusing it to crimp it onto a recording medium is known. In the fixing device, an outside magnetic member and an inside magnetic member are located so as to face to each other inside and outside an excitation coil. Then, each magnetic member is composed of a plurality of divided blocks and they are located in a staggered pattern so as to complement spaces between the blocks of both the magnetic members at constant intervals. In addition, temperature detecting member and an energization interrupting member are located between the block of the magnetic member.
However, in a case of locating the electric components inside the fixing belt, it is necessary to take measures so that magnetic flux generated by temperature inside the fixing belt and the coil does not affect the electric components. Although almost the magnetic flux generated by the coil is absorbed by the fixing belt and a belt guide supporting this fixing belt and converted to heat, a part may penetrate the fixing belt and the belt guide as leaked magnetic flux. Approximately 80% of the magnetic flux generated by the coil is absorbed by a belt base material of the fixing belt and converted to eddy current and almost remained magnetic flux penetrates the fixing belt and is absorbed by the belt guide and converted to eddy current. In the sliding belt IH manner, it is necessary to make the fixing belt being equal to or thinner than. A thickness capable of maintaining flexibility and it is preferable to make the belt guide in a thickness of nearly 0.2 mm in order to reduce spring performance and heat capacity of the fixing belt as low as. Accordingly, because the magnetic flux leaked inside the fixing belt does not become completely 0, there is a slightly magnetic flux leaked inside the fixing belt. Subsequently, electromagnetic noise may occur by the leaked magnetic flux to affect wiring of a lead wire pulled out from the electric components located inside the fixing belt.
As the electric components, for example, there are a temperature sensor, such as a thermistor contacting the inside of the fixing belt, a safety element, such as a temperature fuse contacting the inside of the fixing belt, and others. As mentioned above, a configuration reducing an effect of the electromagnetic noise by locating the wiring of the electric components at an area less affected by the leaked magnetic flux is proposed.
Incidentally, in the sliding belt IH manner, a thermostat is applied as the safety element. The thermostat is generally wired by pulling out lead wires from both sides of a temperature sensing part, such as bimetal. If the thermostat is located inside the fixing belt, the lead wires are pulled out from both ends of the fixing belt, and then, routed so as to surround a belt unit, thereby making large loops. The wiring of the lead wired with such large loops causes easily interlinkage of the leaked magnetic flux from the coil, that is, is easily affected by the electromagnetic noise generated by the leaked magnetic flux, and therefore, the electromagnetic noise becomes large relatively.